Practical 3 : Particle Size and Shape Analysis using Microscope

PART B

Title : Particle size and shape analysis using microscope

Objectives

1.  To analyse and differentiate  the different sizes and shapes of particles (sands and powders) under microscope.
2. To describe and discuss the distribution of the particles size and shape.

Introduction

There are actually various methods that can be used to determine the sizes and shape of particles.Microscopic method is one of the most simple and are widely used method in this experiment.It can be used to determine the size,diameter,shape and surface area that cannot be determine accurately by our visual eyes.

For this experiment,different sizes and shapes of sand and powders had been used.For the sands.we used 50 mic,355 mic,500 mic.850 mic and various type of sands while we used lactose and MCC for the powders.Each sample was observed under the microscope and all the result was taken at the end of the experiment.

Sand is a naturallya granular material composed of finely divided rock and mineral particles.It exists in various different sizes ranging from 0.0625 mm to 2 mmThere are two type of sand which is fine sand and course sand.Fine sand was defined as particles between 0.02mm and 0.2mm while course sand are between 0.2mm and 2.0mm.It is used in the experiment because it is inert,easy to handle and obtain and economical.

For the powders used in this experiment are lactose and microcrystalline cellulose (MCC).MCC is one of the most important and widely used of all expicients.It is a key diluent for drug formulations and an essential component for almost every kind of oral dosage including tablets,capsules,sachets,pellets and others,as well.Lactose also one of most important expicients in tablet formulation nowadays.

Material and Apparatus

glass slide and cover slides

microscope

different type of sand and powders

Procedure

1.  Samples of different size of sands which are 50 mic,355 mic,500 mic,850 mic and various type of sand were taken.Then,2 powder which are lactose and MCC was taken as sample too.
2.  Each sample was place on the glass slide and were observed under the microscope with the same magnification which is 4x. 
   
   
3. The shape and size of the particles were observed and taken at the end of the experiment.
4.  Differences between the size and shape of the sands and powders were discussed and recorded.

Result

Particles & Size	Shape	Characteristics
Sand : 50 mic		·         Have the smallest size      ·         irregular in shape      ·         almost have constant  size      ·     mostly round,some sharp and   pointed              edges
Sand : 355 mic		·         size is bigger than 50 mic      ·         size is irregular      ·         almost same size      ·         some sharp and pointed edges
Sand : 500 mic		·         size bigger tha 355 mic      ·         irregular in shape      ·         almost the same size      ·         contains sharp edges
Sand : 850 mic		·         size larger among other sand      ·         irregular in shape      ·         almost same size      ·         very sharp edges
Various type of sands		·         different in the size       ·         irregular shape      ·      some round shape,some sharp and some have very pointed edges
Lactose		·         the size is constant      ·         very fine      ·         round and needle-like      ·         regular shape      ·         do not have sharp edge
MCC		·         have the smallest size and fine      ·         size is almost constant      ·         mostly round      ·         regular shape      ·         edges do not pointed out

      

      Question

    1.Explain in brief the various statistical methods that you can used to measure the diameter of a particle.

The methods that can be used to measure the diameter of a particle are laser diffraction, dynamic light scattering, automated imaging, sedimentation and sieving. When a laser beam passes through a dispersed particle, laser diffraction instrument can determine the diameter of particle by measuring the variation of angle in intensity of light scattered. The smaller the particle, the larger the angle of light scattered and vice versa. The angular scattering intensity data is taken to calculate the size and diameter of the particles according to the scattering pattern created by using the Mie theory of light scattering. The second method is dynamic light scattering (DLS) which used to measure size of particle samples that suspended in liquid like protein, colloidal dispersions and emulsion. If a particle is illuminated with a laser light, the particle will scattered the light. The intensity of scattered light fluctuates over short timescales which its rate is depend on the size of particle. The smaller particle is displaced further from the solvent molecules and can move more rapidly. The intensity fluctuation of light scattered is detected by a detector and converted into electrical pulses, which are fed into the digital correlator. Then, the size and diameter of the particle can be calculated. Next, automated imaging is a high resolution direct technique for measuring the particles from around 1 micron up to several millimeters in size. An individual particle images are captured from dispersed samples and are analyzed to determine their size, shape and other physical properties. Additionally, sedimentation method determine the particle size as a function of settling velocity because it study the terminal velocity of particles suspended in  viscous liquid. The time of sedimentation of finest particle is longest, so this method is suitable for measuring the particle size below 10µm. Lastly, sieving method is widely used to measure diameter of particle due to low cost, easy-interpreting and simplicity by just shaking the sample in sieve tube until the amount retained in each trays is become almost constant.  This technique is suitable for bulk materials and a large amount of materials can be readily loaded into 8-inch-diameter (200 mm) sieve trays.

    

     2. State the best statistical method for each of the samples that you have analysed.

           The best statistical method to measure diameter of particle is laser diffraction method due to some reasons. It has wide dynamic range which can measure particle size from submicron to millimeter size range. The particle diameter can be generated faster within 1 minute. Large number of particles can be sampled in each measurement and hundreds of samples can be measured every day. Next, this method also produce instant feedback as it can monitor and control the particle dispersion process. The calibration is unnecessary as it is easy to be verified by using standard reference materials.

      Discussion

From the experiment, we can observe that MCC has the smallest size of particle, followed by lactose, 150 micron of sand, 355 micron of sand, 500 micron of sand and 850 micron of sand. The powder used in this experiment are lactose and MCC. The size of lactose is almost constant, mostly round, fine and has a regular shape. The size of lactose is also almost constant, fine and has regular shape which is needle like. However, all the sand sample used (150 mic, 355 mic, 500 mic, 850 mic sand) have almost the same size but with irregular shape. Some of the sand have sharp edges while some of the sand have pointed edges. When various type of sand are sampled and observed under microscope, they have different shape and size. Their shape are irregular, some have pointed edges, sharp edges and round in shape.

There are some precaution steps need to be taken in this experiment. In order to compare the size and the shape of sample used, magnification of the lens used must be the same which is 40x to make the comparison of size and shape between different particles easily. The light intensity of the microscope used must be high enough to observe and see the size and shape of sample (sand, lactose and MCC) clearly and easily. Label the weighing boat with the sample to prevent errors during the experiment in order to increase the accuracy of results obtained.

In this experiment, microscope are used to determine, analyse and compare the size and shape of the sample which is the simplest method when compared to other techniques like laser diffraction technique and sieving. However, this method sometime is inaccurate if 2 different particles with almost the same size and same shape are compared because microscope unable to measure the actual size of the particle accurately. Thus, a more suitable technique is recommended which is laser diffraction technique. It has wide dynamic range which can measure particle size from submicron to millimeter size range. The particle diameter can be generated faster within 1 minute. Large number of particles can be sampled in each measurement and hundreds of samples can be measured every day. Next, this method also produce instant feedback as it can monitor and control the particle dispersion process. The calibration is unnecessary as it is easy to be verified by using standard reference materials.

      Conclusion

            Microcrystalline cellulose (MCC) has the smallest size of particle, followed by lactose, 150 micron of sand, 355 micron of sand, 500 micron of sand, 850 micron of sand. Thus, the powder form of particle normally has smaller size than sands. The shape of MCC is fine, mostly round and regular. The shape of lactose is needle-like, fine and regular while the shape of sand is irregular, some have pointed edges, sharp edges or round in shape.

      Reference

   1.      http://golik.co.il/Data/ABasicGuidtoParticleCharacterization%282%29_1962085150.pdf

   2.      http://www.drugs.com/inactive/microcrystalline-cellulose-48.html

   3.      http://www.elmhurst.edu/~chm/vchembook/546lactose.html

  4.    Michael E.Aulton, 2007, Aulton's Pharmaceutics The Design And Manufacture Of    Medicines, Third Edition, Churchill Livingstone Elsevier (page 122-134)